Cytological, immunohistological and immunocytological methods will be used to investigate the role of different trophoblast populations during implantation in the macaque, and to compare these observations with those in two species, the rat and horse, exhibiting different patterns of epithelial and stromal invasion. The role of fetal-maternal cell fusion in expansion of trophoblast along the plane of the epithelium will be studied in the macaque using cytological and cell marker techniques. The extent of linkage between cytotrophoblast cells and cytotrophoblast cells and syncytial trophoblast will be studied using antibodies to junctional complex constituent proteins in this species. DNA synthesis in trophoblast populations will be examined using 3H thymidine incorporation in vitro in macaque implantation sites. The role of selected cell adhesion molecules in interaction of trophoblast and uterine tissues will be followed using antibody methods during implantation and early placentation in the macaque and rat. As a means of characterizing different trophoblast populations and providing functional implications the distribution of lysosomal and nonlysosomal lytic enzymes will be mapped in macaque trophoblastic plate to anchoring villous stages. Surface modifications and differentiation of equine girdle cells will be examined as they relate to migration of these cells into the endometrium. Adhesion molecules also will be studied in relationship to segregating cell populations in the uterus and trophoblast of the rat during implantation and early placentation. Adhesion molecules between trophoblast cells and endothelial cells will be localized to establish their role in formation of vascular patterns in the macaque and rat, and the manner in which equine trophoblast cells invade lymphatic vessels but not capillaries will be examined. Finally, embryos obtained during the macaque studies will be used to examine the manner of formation of the secondary yolk sac and the contribution of the prochordal plate and notochordal process to the establishment of definitive intraembryonic endoderm. It is believed that these studies can make a substantial contribution to our understanding of the way in which trophoblast cells can interact with the endometrium during the crucial implantation stages preceding placentation.